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Validation des produits d'inversion des observations satellitaires CALIPSO/CloudSat pour la caractérisation des propriétés optiques et microphysiques des nuages de glace et en phase mixte

Abstract : This study is part of the validation projects of CALIPSO and CloudSat satellites which are devoted to the observation of clouds in the A-Train constellation, in order to improve clouds parameterisations in climate forecasting models. Our work is based on in situ airborne measurements (PMS, Polar Nephelometer, CPI) of microphysical and optical properties of clouds. Several field campaigns have been made in Arctic region (ASTAR 2007 and POLARCAT), and in mid-latitude cirrus (CIRCLE-2) during which in situ observations have been collocated with satellites observations. CPI data processing has been improved for the determination of microphysical properties and for the calculation of a radar reflectivity factor (Z). Concerning CALIPSO validation, two cirrus situations show a good agreement between in situ and retrieval extinction coefficients (σ), and so validate the hypothesis made in the lidar retrieval method. In another situation, orientation effect of ice crystal with planar shape leads to specular reflexions of the laser beam and consequently to an overestimation of σ retrievals. On the contrary, larger in situ values of σ are observed during a situation where large ice crystals are present. Shattering effects of these crystals could generate small particles inducing an overestimation of in situ σ. Concerning CloudSat validation, the results show a good agreement between ZCloudSat et ZCPI. However, cloud products retrievals are widely overestimate in particular in mixed phase clouds where the retrieval scheme based on temperature seems to give bad values.
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Guillaume Mioche. Validation des produits d'inversion des observations satellitaires CALIPSO/CloudSat pour la caractérisation des propriétés optiques et microphysiques des nuages de glace et en phase mixte. Océan, Atmosphère. Université Blaise Pascal - Clermont-Ferrand II, 2010. Français. ⟨NNT : 2010CLF22026⟩. ⟨tel-00719316⟩

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